Tissue distribution of vitamin E metabolites in rats after oral administration of tocopherol or tocotrienol

We previously found that 2,7,8-trimethyl-2(2'-carboxyethyl)-6-hydroxychroman (γCEHC), a metabolite of the vitamin E isoforms γ-tocopherol or γ-tocotrienol, accumulated in the rat small intestine. The aim of this study was to evaluate tissue distribution of vitamin E metabolites. A single dose of α-tocopherol, γ-tocopherol or a tocotrienol mixture containing α- and γ-tocotrienol was orally administered to rats. Total amounts of conjugated and unconjugated metabolites in the tissues were measured by HPLC with an electrochemical detector, and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox) was used as an internal standard. Twenty-four hours later, the vitamin E isoforms were detected in most tissues and in the serum. However, 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (αCEHC), a metabolite of α-tocopherol or α-tocotrienol, and γCEHC accumulated in the serum and in some tissues including the liver, small intestine and kidney. Administration of α-tocopherol increased the γCEHC concentration in the small intestine, suggesting that α-tocopherol enhances γ-tocopherol catabolism. In contrast, ketoconazole, an inhibitor of cytochrome P450 (CYP)-dependent vitamin E catabolism, markedly decreased the γCEHC concentration. These data indicate that vitamin E metabolite accumulates not only in the liver but also in the small intestine and kidney. We conclude that some dietary vitamin E is catabolized to carboxyethyl-hydroxychroman in the small intestine and is secreted into the circulatory system.     

In vivo angiogenesis is suppressed by unsaturated vitamin E, tocotrienol

Antiangiogenic therapy using drugs and food components is a recognized strategy for the prevention of various angiogenesis-mediated disorders such as tumor growth, diabetic retinopathy, and rheumatoid arthritis. Our preliminary cell culture studies, using both bovine aortic endothelial cells and human umbilical vein endothelial cells (HUVEC) on screening for food-derived antiangiogenic compounds, showed tocotrienol (T3), an unsaturated version of vitamin E, to be a potential angiogenic inhibitor. We therefore investigaged the in vivo antiangiogenic properties of T3 using 2 well-characterized angiogenic models [mouse dorsal air sac (DAS) assay and the chick embryo chorioallantoic membrane (CAM) assay]. In the DAS assay, the increased neovascularization (angiogenesis index, 4.8 +/- 0.6) in tumor cell-implanted mice was suppressed (angiogenesis index, 2.7 +/- 0.6) by dietary supplementation of 10 mg T3-rich oil/d (equivalent to 4.4 mg T3/d). In the CAM assay, T3 (500-1000 microg/egg) inhibited new blood vessel formation on the growing CAM and increased the frequency of avascular zone (36-50%). To evaluate the antiangiogenic mechanism, we conducted cell-culture studies and found that T3 significantly reduced fibroblast growth factor -induced proliferation, migration, and tube formation in HUVEC (P < 0.05), with delta-T3 having the highest activity. Western blot analysis revealed that delta-T3 suppressed the phosphorylation of phosophoinositide-dependent protein kinase (PDK) and Akt, and increased the phosphorylation of apoptosis signal-regulating kinase and p38 in fibroblast growth factor-treated HUVEC, indicating that the antiangiogenic effects of T3 are associated with changes in growth factor-dependent phosphatidylinositol-3 kinase /PDK/Akt signaling as well as induction of apoptosis in endothelial cells. Our findings suggest that T3 has potential as a therapeutic dietary supplement for preventing angiogenic disorders, and therefore future clinical study will be required to evaluate the efficacy and safety of T3.     

Synergistic effects of tocopherol, tocotrienol, and ubiquinone in indomethacin-induced experimental gastric lesions

Nonsteroidal anti-inflammatory drugs and their adverse effects on the gastric mucosa are yet another set of unresolved medical problems. This study examined the effects of various antioxidants on several gastric parameters after a single exposure to indomethacin. Forty-eight male rats of the Sprague-Dawley (200-250 g) strain were randomly divided to receive a single antioxidant (tocopherol, tocotrienol, or ubiquinone) or a combination of two (tocopherol-tocotrienol, tocopherol-ubiquinone or tocotrienol-ubiquinone) for 28 days. The rats were then challenged with a single dose of indomethacin and killed six hours later. Findings showed that the severity of gastric lesions was comparable in all groups. Only groups that received a combination of antioxidants exhibited reduced lipid peroxidation compared with all other groups (p < 0.05). The combination groups had a higher level of gastric prostaglandin E2 (PGE2) content compared with all other groups (p < 0.05). There was no significant difference among the groups in the gastric acid concentration and the glutathione/oxidized glutathione (GSH/GSSG) ratio. We conclude that although supplementation of these antioxidants in combination had desirable effects on lipid peroxidation and gastric PGE2 level, they did not reduce the lesions produced by indomethacin.     

A rapid procedure for analysing rice bran tocopherol,tocotrienol and γ-oryzanol contents

Tocopherols, tocotrienols and γ-oryzanol compounds are phytochemicals with antioxidant activities and potential health benefits. Their contents and isomer ratios in rice bran vary among southern US cultivars, suggesting that breeding for higher contents or a favorable ratio of these phytochemicals is feasible. Methods that can rapidly and reliably extract and quantify their contents in rice bran or whole rice kernel are necessary for breeding programs. A simple, one-step equilibrium extraction procedure coupled with reversed-phase (RP) HPLC is presented here. The one-min equilibrium extraction at a 1:60 (w/v) ratio of rice bran to methanol recovered 92 to 102% of the target phytochemicals relative to those of repeated, non-saponified, direct solvent extraction methods. At this 1:60 ratio of bran to solvent, isopropanol and methanol are superior extraction solvents relative to hexane. A modified, mobile-phase gradient with 10% of aqueous phase for the first 3-min eliminates all the methanol-soluble interfering compounds. This extraction method has the following advantages over the currently available methods: speed, no special extraction instrumentation is needed; and the extraction solvent, methanol, is compatible with subsequent quantification via RP-HPLC.     

Serum selenium, vitamin A, vitamin E and cholesterol concentrations in Finnish and Japanese postmenopausal women

Serum concentrations of vitamins A and E, selenium, and cholesterol were measured in 30 Finnish and 30 Japanese postmenopausal women. While both groups had identical serum vitamin A levels, the other serum factors differed significantly between the groups, the Finns having higher serum vitamin E and cholesterol and lower serum selenium levels. Adjusted to serum cholesterol, which correlated significantly with vitamin E in both groups, the vitamin E levels were, however, similar in the groups. The differences in the serum levels of these nutritional factors may be associated with the differences in the risk of coronary heart disease and cancer between Finnish and Japanese populations.     

Serum 25-OHD, vitamin A and vitamin E concentrations in healthy Finnish and Floridian women

The concentrations of 25-hydroxyvitamin D (25-OHD), vitamin A and vitamin E were measured in serum samples of Finnish and Floridian women; the samples were collected in spring. The Floridians had twice as much 25-OHD in serum as the Finns, but the levels of the two other fat-soluble vitamins were equal. Thus, in Florida there is very little risk for vitamin D deficiency, and vitamin A and E status seems to be unaffected by differences in dietary habits.     

gamma-tocopherol, the major form of vitamin E in the US diet, deserves more attention.

gamma-tocopherol is the major form of vitamin E in many plant seeds and in the US diet, but has drawn little attention compared with alpha-tocopherol, the predominant form of vitamin E in tissues and the primary form in supplements. However, recent studies indicate that gamma-tocopherol may be important to human health and that it possesses unique features that distinguish it from alpha-tocopherol. gamma-Tocopherol appears to be a more effective trap for lipophilic electrophiles than is alpha-tocopherol. gamma-Tocopherol is well absorbed and accumulates to a significant degree in some human tissues; it is metabolized, however, largely to 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), which is mainly excreted in the urine. gamma-CEHC, but not the corresponding metabolite derived from alpha-tocopherol, has natriuretic activity that may be of physiologic importance. Both gamma-tocopherol and gamma-CEHC, but not alpha-tocopherol, inhibit cyclooxygenase activity and, thus, possess antiinflammatory properties. Some human and animal studies indicate that plasma concentrations of gamma-tocopherol are inversely associated with the incidence of cardiovascular disease and prostate cancer. These distinguishing features of gamma-tocopherol and its metabolite suggest that gamma-tocopherol may contribute significantly to human health in ways not recognized previously. This possibility should be further evaluated, especially considering that high doses of alpha-tocopherol deplete plasma and tissue gamma-tocopherol, in contrast with supplementation with gamma-tocopherol, which increases both. We review current information on the bioavailability, metabolism, chemistry, and nonantioxidant activities of gamma-tocopherol and epidemiologic data concerning the relation between gamma-tocopherol and cardiovascular disease and cancer.     

Influence of eicosapentaenoic acid and vitamin E on hepatic hydroxyproline content in rabbits fed cholesterol-rich diet

The effect of eicosapentaenoic acid (EPA) and vitamin E on hepatic hydroxyproline content, as an index of collagen was examined in rabbits receiving cholesterol rich diets for a period of 45 days. Rabbits were divided as control (A) and cholesterol fed groups (B, C, D). Group C received 80 mg. of EPA and group D received 100 IU of vitamin E daily in addition to the cholesterol rich diet (2% w/w) which was solely given to group B. The maintenance of rabbits on high cholesterol diets resulted in significantly increased liver cholesterol concentrations. This effect was most pronounced in rabbits receiving cholesterol alone. Hepatic triglyceride levels remained unchanged in all cholesterol-fed rabbits, but total phospholipid levels in liver significantly decreased in EPA and vitamin E supplemented rabbits. An interesting finding was the increase in hepatic hydroxyproline content in rabbits following the administration of EPA and vitamin E to cholesterol rich diet.     

Effect of feeding polyunsaturated fatty acids with a low vitamin E diet on blood levels of tocopherol in men performing hard physical labor.

A diet made low in vitamin E by elimination of foods considered good sources of the vitamin was fed for 13 months to two groups of men engaged in strenuous labor. With a daily average dietary intake of about 9.4 mg of total tocopherols, a progressive decline in blood levels of tocopherol from 1.42 to 0.81 mg/100 ml was observed in the five control subjects. The test group of 30 men received a daily supplement of tocopherol-stripped safflower oil containing 88 g of polyunsaturated fatty acids and 2.3 mg of tocopherols. Average blood plasma levels of tocopherol in this group dropped rapidly from an initial value of 1.01 to about 0.5 mg/100 ml within 5 months and remained relatively stable thereafter. No muscular weakness or other physical symptoms were reported.     

Comparison of a vitamin E-rich diet and supplemental vitamin E on measures of vitamin E status and lipoprotein profile

OBJECTIVE: To determine whether dietary modification rather than use of supplements can raise indices of vitamin E status to potentially cardioprotective levels. DESIGN: Eight week randomised controlled trial with parallel treatments to compare increased use of vitamin E-rich foods, supplementation with 200 IU of vitamin E, and a placebo. SETTING: Dunedin, New Zealand. SUBJECTS: Ninety subjects were recruited, of whom 82 non-smoking, free-living individuals aged 22-72 y with plasma cholesterol <7.5 mmol/l completed the trial. MAIN OUTCOME MEASURES: Dietary intakes, plasma alpha tocopherol, plasma alpha tocopherol/cholesterol ratio and lipoprotein cholesterol. RESULTS: Consumption of an additional 12 mg of vitamin E (alpha tocopherol equivalents) from dietary sources was primarily achieved through the replacement of saturated fat-rich foods with unsaturated fats rich in vitamin E, nuts and vegetables. This resulted in a 3.4 micromol/l increase in plasma alpha tocopherol at week 6 (95% CI 1.6-5.3), and 0.9 micromol/mmol in plasma alpha tocopherol/cholesterol at weeks 4 and 6 (95% CI 0.3-1.4 and 0.4-1.4, respectively) when compared with the placebo group. In the supplement group, plasma alpha tocopherol and plasma alpha tocopherol/cholesterol were significantly increased within 2 weeks and remained so throughout the 8 week intervention. CONCLUSION: Increasing dietary vitamin E intake can increase plasma alpha tocopherol levels, although factors other than dietary intake are also important determinants. The extent of dietary modification required to achieve potentially cardioprotective levels of plasma alpha tocopherol is difficult in practice. SPONSORSHIP: The study was supported through the Otago Medical Research Foundation Laurenson Award.     

Effect of intraperitoneally injected tocopherol on vitamin E status of dairy cow

The effect of intraperitoneal (IP) administration of vitamin E on the concentration of tocopherol in the blood and milk of cows was studied. Two trials were carried out using a total of twenty-four Holstein cows. In the first trial, two doses of dl-alpha-tocopherol (1 g and 5 g) were given to six cows in each treatment. Administration of 1 g caused a small increase in blood and milk concentrations; dosing with 5 g IP caused appreciable increases in both plasma and milk concentrations. Plasma and milk concentrations peaked 1 d after dosing with a maximum value of 10.7 micrograms/ml plasma and 1.39 micrograms/ml milk. Then there was a continuous decline during the 14 d experimental period. In the 2nd trial, twelve cows were dosed IP with the acetate form of vitamin E. Six cows were given 5 g and six others 10 g of dl-alpha-tocopherol acetate. Maximum plasma vitamin E concentrations occurred at d 2 (7.4 micrograms/ml) and d 1 (10.9 micrograms/ml) for the cows dosed with 5 and 10 g of the ester form, respectively. Milk vitamin E concentrations were significantly higher (P less than .05) during the first 4 d for cows dosed with 10 compared to those given 5 g. During the 14 d experimental period, maximum milk vitamin E concentration for the 10 g group was 141 micrograms vitamin E/g fat 2 d after dosing and for the 5 g group 62 micrograms vitamin E/mg fat also at 2 d after dosing. The technique of dosing cows with vitamin E by IP proved to be an effective way for increasing vitamin E status. These treatments had no effect on cholesterol content of milk fat. However, it was noted that cholesterol level was lower in PM milking as compared to AM milking.     

Dose dependent elevation of plasma tocotrienol levels and its effect on arterial compliance, plasma total antioxidant status, and lipid profile in healthy humans supplemented with tocotrienol rich vitamin E

Tocotrienols are a class of vitamin E reported to be potent antioxidants, besides having the ability to inhibit the HMG-CoA reductase enzyme. This study assessed the effects of 3 doses of tocotrienol-rich vitamin E (TRE) on plasma tocotrienol isomer concentration, arterial compliance, plasma total antioxidant status (TAS), aortic systolic blood pressure (ASBP), serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) in healthy males. METHODOLOGY: This randomised, blinded end-point, placebo-controlled clinical trial with a parallel design involved 36 healthy male subjects who took either an oral placebo or TRE at doses of 80, 160 or 320 mg daily for 2 mo. Baseline and end-of-treatment measurements of vitamin E concentration, arterial compliance [assessed by aortic femoral pulse wave velocity (PWV) and augmentation index (AI)], ASBP, plasma TAS, serum TC and LDL-C were taken. RESULTS: Baseline tocotrienol isomer concentrations were low and not detectable in some subjects. Upon supplementation, all TRE-treated groups showed significant difference from placebo for their change in alpha, gamma and delta tocotrienol concentrations from baseline to end of treatment. There was a linear dose and blood level relationship for all the isomers. There was no significant difference between groups for their change in PWV, AI, plasma TAS, ASBP, TC or LDL-C from baseline to end of treatment. Groups 160 mg (p = 0.024) and 320 mg (p = 0.049) showed significant reductions in their ASBP. Group 320 mg showed a significant 9.2% improvement in TAS. CONCLUSION: TRE at doses up to 320 mg daily were well tolerated. Treatment significantly increased alpha, delta, and gamma tocotrienol concentrations but did not significantly affect arterial compliance, plasma TAS, serum TC or LDL-C levels in normal subjects.